1. Field of the Invention
The present invention relates to an optical recording/reproducing apparatus, and more particularly to an optical recording/reproducing apparatus employing an evanescent wave generating lens for recording and reproducing information signals to and from an optical recording media, such as an optical disk.
2. Discussion of the Background
Today, in the field of information recording, a variety of technological advances have been made for high-density recording. In order to achieve the intended high-density information recording in a limited region of recording medium, a light beam emitted from a laser beam source, such as a semiconductor laser, is reduced or minimized in spot size. One approach to fulfilling such demands is to employ a recently developed recording/reproducing technique which makes use of evanescent wave to form a minuscule laser spot on the medium.
This technique is designed to employ a specific type of lens capable of generating an evanescent wave (referred to as the "evanescent wave generating lens" hereinafter), which utilizes an evanescent wave that is producible due to the total internal reflection of light inside the lens. Note that the evanescent wave generating lens is generally called a solid immersion lens (SIL) among those skilled in the art. The resultant evanescent wave produced by such lens is capable of forming a fine or sub-micro spot on the surface of an optical recording medium used, such as an optical disk, which in turn increases the recording density of information being recorded on the recording medium.
However, the prior known approach encounters a problem in that the efficiency of evanescent wave generation remains deficient.
FIG. 1 is a diagram schematically depicting a prior art optical system which employs a hemispherical lens acting as the evanescent wave generating lens. As shown herein, rays of incident light are collected by an objective lens 101 and guided to perpendicularly enter the curved surface of an evanescent wave generating lens 102, and then are focused inside the hemispherical lens 102 for forming a light spot on the recording surface of a recording medium 103 via evanescent wave. The evanescent wave generating lens 102 is a hemispherical lens.
FIG. 2 is a graph showing a normalized distribution profile of the normalized beam intensity of the light spot of the optical system of FIG. 1. The intensity distribution is obtained both the hemispherical lens 102 and the recording medium 103 are set at approximately 1.88, an air gap distance between the hemispherical lens 102 and the recording medium 103 is about 0.3 times the wavelength of incidence light, and the incidence angle of "marginal" light rays inside the hemispherical lens 102 is set at 57.6 degrees. Note here that the horizontal axis of the graph of FIG. 2 represents positions (q/.lambda.) as measured along the radial direction inside the surface of the recording medium 103.
It is understood from FIG. 2 that the resulting intensity distribution of beam spot has a plurality of peaks along the radial direction inside the surface of the recording medium 103, including one central maxima and two smaller peaks on its opposite sides. These side peaks are called the "sidelobes" by one skilled in the art. Sidelobes may lower optical resolution.
In this way, the prior art optical system suffers from a problem: it remains difficult to readily increase the optical resolution of the recording/reproducing apparatus due to generation of such sidelobes.
The present invention has been made in view of the above, and a primary object of the present invention is to provide an improved optical recording/reproduction apparatus with improved optical resolution.